Heretofore as cationic flotation collectors intended mainly for minerals, hydrochlorides and acetates of such long-chain alkylamines as lauryl amine, tallow amine, and coconut amine have been finding extensive utility.
The flotation collectors (hereinafter referred to briefly as "collectors") based on such long-chain alkylamine salts as mentioned above are deficient in the efficiency for recovery and separation of valuable inorganic substances in the flotation. Particularly, they have a disadvantage that their capacity for performance is greatly impaired by the conditions of flotation such as concentration of co-existing water-soluble inorganic salts, pH and temperature of the water system. The impairment of the capacity for performance is conspicuous when the water system happens to contain water-soluble inorganic salts represented by chlorides, sulfates, carbonates, and phosphates of sodium, potassium, calcium, magnesium, manganese, iron, and aluminum on the order of several thousand ppm. Particularly when the water system subjected to the flotative treatment has a high salt concentration and a high temperature exceeding 70.degree. C like the geothermal water, these collectors effect the recovery only with a low coefficient and can hardly be expected to provide effective flotation. Further, since the long-chain alkylamine salt type collectors have their qualities notably affected by variation in the pH value of the water system, the possible impairment of the capacity is generally precluded by optimizing the pH value of the water system by addition of a pH adjusting agent. This pH adjustment complicates the operation of the flotative treatment and jeopardizes the ease of use of collector.
In the circumstances, the desirability of developing a flotation collector capable of fully manifesting the capacity thereof in effecting flotative recovery and separation at high levels never attained by the conventional collectors even in a water system of high temperature or a water system susceptible of wide pH variation, irrespectively of the amount of water-soluble inorganic salts present in the water system under treatment has been finding recognition.
In recent years, efforts are being continued to promote the utilization of the geothermal water as a stable and clean energy source of lasting reserve. In the utilization of the geothermal water, since the temperature of the geothermal water never fails to fall during the course of the utilization, the inorganic substances, particularly silica, which are retained in a dissolved state in the geothermal water at the initial high temperature are suffered to precipitate in a large amount. These precipitated inorganic substances bring about a serious disadvantage that they are deposited in the form of scale in conduits, heat exchangers, return wells, etc.
To prevent the deposition in the piping of the scale formed mainly of silica (hereinafter referred to as "silica type insoluble component"), various measures are being tried including:
(1) A method which comprises adding an acid to the geothermal water thereby lowering the pH value thereof.
(2) A method which comprises adding a compound of such a polyvalent metal as aluminum, iron, or calcium to the geothermal water thereby inducing aggregation and precipitation of the silica type insoluble component therein.
(3) A method which comprises introducing the geothermal water into a retention tank and retaining it therein until the silica type insoluble component thoroughly aggregates and precipitates therein.
(4) A method which comprises adding such a chemical agent as a surfactant, a water-soluble polymer, an inorganic or organic phosphate, or a chelating agent to the geothermal water thereby inhibiting precipitation of inorganic substances, particularly silica.
(5) A method which comprises adding a cationic surfactant based on a long chain alkyl amine such as lauryl amine salt or tallow amine salt to the geothermal water thereby effecting flotative removal of the silica type insoluble component therefrom.
The method of (1), however, suffers as a problem the corrosion of piping due to the fall of the pH value. The methods of (2) and (3) are uneconomical because of the heavy energy loss suffered to occur during the course of aggregation and precipitation. The method of (4) is not sufficiently effective in thoroughly inhibiting the precipitation of the inorganic substances. The method of (5), though comparatively effective where the amount of inorganic ions present in the geothermal water is small, is not sufficiently effective in flotative removal where the amount of inorganic ions is large. Generally the geothermal water contains a large amount of inorganic ions. No desirable results are obtained, therefore, by increasing the amount of the cationic surfactant to be added. Further, failure to control the pH value at the optimum level results in impairment of quality.
Since the conventional methods suffer from numerous drawbacks, the desirability of developing an economical and feasible method for the treatment of the geothermal water has been finding growing recognition.
An object of this invention, therefore, is to provide a flotation collector for inorganic substances which is not appreciably affected by the presence of water-soluble inorganic salts in a water system under treatment or by the condition of temperature and pH of the water system but is permitted, even at a low application rate, to manifest an outstanding effect in attaining flotative recovery and selection at high levels.
Another object of this invention is to provide a method for the treatment of geothermal water which attains effective separation and removal of the silica type insoluble component which is precipitated in the geothermal water during the utilization of the geothermal water, thereby precluding the otherwise inevitable deposition of the silica type insoluble component in the piping and facilitating the utilization of the geothermal water.